It is important to determine the occurrence of leaks and other similar events because they result in the loss of valuable products stored in the tanks or conveyed in the pipes. Additionally, many of the fluids stored in the tanks or transported in pipes are hazardous to life and property, may be flammable, and may be toxic. They may be incompatible with living matter in a variety of ways. The loss of valuable product as well as the damage to the environment, life and property generally increases with the quantity of fluid that escapes between the inception of the leak and the time it is contained. Consequently early detection of leaks is important. The results are smaller losses of product and hence less difficult and less expensive cleanup and remediation.
Various methods have been developed to detect the occurrence of such leaks. These methods may be categorized as internal and external methods. The methodology that is the subject of the present invention is categorized as an external method.
Internal methods rely on measurements made on the fluid in the tank itself. They necessarily interfere with the fluid within the tank. External methods monitor the tank's environment for leak associated occurrences.
External methods have advantages over internal methods. They avoid invasion of the storage environment, allow leak detection without interfering with flow of fluid into and out of the vessel, and they more easily continuously monitor the vessel for leakage, particularly when dealing with existing tank installations.
One common method of external storage vessel leak detection is to utilize a double walled tank with sensors between the two walls. This method is often inadequate due to the substantial expense involved, particularly when dealing with existing tank installations.
Another common method of external storage vessel leak detection disclosed in U.S. Pat. No. 4,835,522, involves using monitoring equipment in subsurface wells around the tank (vadose monitoring) and in some cases atmospheric monitors located around the tank. Monitoring equipment generally consists of sensors that react to the fluid in the tank and some means of measuring the output signal from these sensors. When the sensors detect the presence of the fluid stored in the tank they respond and the monitoring equipment produces a leakage alarm signal.
This methodology works quite well when there is no precontamination. In such a situation the sensor reads near zero in the absence of a leak, and readings rapidly rise to large values when the leak occurs. However, when a leak has previously occurred, some of the leaked fluid generally remains in the tank and sensor environment even after most of the lost product has been reclaimed. How much remains depends on the fluid that leaked, the specific cleanup and remediation methods employed, and the nature of the contaminating material.
When the sensors are already detecting some of the lingering substance, present leak detection methods are inadequate. Changes in temperature and ground water levels can significantly alter sensor readings signalling a leak when one does not exist.
The method and apparatus of this invention more effectively filter out natural fluctuations of the monitored substance concentration and still respond to leaks when they occur.
The following prior art reflects the state of the art of which applicant is aware and are included herewith to discharge applicant's acknowledged duty to disclose relevant prior art. It is stipulated, however, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
______________________________________ INVENTOR PATENT NO. ISSUE DATE ______________________________________ Farmer 4,796,466 January 10, 1989 Furuse 4,670,847 June 2, 1987 ______________________________________
The system of the Farmer patent utilizes statistical methods to distinguish a signal representing a pipeline leak from signals representing normal pipeline functions and other noise.
The Furuse patent discloses an internal leak detection method involving comparing pressure data on a tested tank with tested data on any identical tank known to be leak free. Furuse uses an error correction algorithm to improve the reliability of the pressure readings.
The invention of this application is distinguishable from Furuse in many ways. External readings of contained fluid concentration are made rather than internal pressure readings. Also, this invention is operatable without any requirement of a leak free tank as a control for the test.
The method of this application is distinguishable in that sensors are located external to the vessel being monitored and also this method analyzes concentration data rather than pressure or velocity data as analyzed in the Farmer patent. Usually a containment vessel such as a storage tank has no velocity or pressure to be analyzed and the Farmer patent would not be applicable.